The present invention relates to a storage system, in particular a disk-based tape emulation storage device.
Data is the underlying resources on which all computing processes are based. With the recent explosive growth of the Internet and e-business, the demand on data storage systems has increased tremendously. There are many types of storage devices, e.g., semiconductor devices, magnetic disk, and magnetic tapes, that may be used to store data. Each of these types of storage devices have different access speeds and costs associated thereto. The semiconductor devices are generally the fastest and also the most expensive. Accordingly, they are not commonly used in data centers where massive amounts of data need to be stored.
Generally, magnetic disks and tapes are the storage devices of choice for the data centers since they tend to be considerably cheaper than the semiconductor devices. The storage system for a data center generally has multiple processors and includes sophisticated operating systems for quickly reading and writing massive amounts of data.
Data centers or storage systems commonly includes a plurality of storage units or subsystems. Some are configured to be primary storage devices, and others are configured to be secondary storage devices. The primary storage devices are designed to store active data that users may access, whereas the secondary storage devices serves as back-up devices to be used in case the primary storage devices experience failure. The secondary devices are also used to store or archive “inactive” or “stale” data that the primary device does not need, so that the storage capacity of the primary devices may be freed-up for new data. As used herein, the term “archiving” refers to copying data from a first storage device to a second storage device and then deleting the data stored in the first storage device, so that the storage capacity of the first storage device is freed-up for new data.
The primary storage device is located at a primary site, and the secondary storage device is located at a secondary site that may be dozens, hundreds, or even thousands of miles apart from the primary site.
The magnetic disk storage devices are commonly used in the primary storage devices for “active” data because access to specific data in a magnetic disk storage device is more rapid than access to data in a magnetic tape device. On the other hand, the magnetic tape devices are used in the secondary storage devices or vaults to archive or back-up data due to its relatively low cost.
However, the use of the magnetic tape devices in the secondary site poses some problems. The “inactive” data need to be copied onto a tape and then the tape physically shipped or delivered to the secondary site. In addition, the archived data cannot be made to the user quickly since they need to be physically transferred back to the primary site and then loaded on the primary device before the users can access them. Moreover, the archived tapes need to be managed by the secondary device and generally cannot be managed remotely using the primary device.